Quantification of Immune Cells in Women Using Contraception Optimally HIV prevention strategies should be linked to contraception for maximal public health benefit. However, hormonal contraception has been associated with increased risk of human immunodeficiency virus (HIV) acquisition and transmission. The underlying biological mechanisms for this association are not fully understood. It is established that progesterone and progestin have effects on the human immune system, including effects on mucosal immunity. Genital tract immune cells are common portals of entry for HIV yet little is known about the effects of these contraceptives on immune cells in the genital mucosa. Given data suggesting women using systemic hormonal contraceptives may have increased susceptibility to HIV; this is a significant knowledge gap. The broad, long-term objectives of the studies proposed here are to clarify the relationship between contraceptive use and risk of HIV acquisition by characterizing changes in T lymphocyte populations in the cervices and endometria of women after initiation of hormonal contraception or intrauterine device (IUD) use. The proposed study aims to quantify immune cells and cell receptors within the female genital tract that are associated with HIV transmission, and to detect changes occurring with use of contraceptives. We plan to recruit a total of 225 healthy women aged 18-34 into a parallel cohort study: fifty each who are interested in initiating use of one of 4 contraceptives: (1) combined oral contraceptive pills, (2) depot medroxyprogesterone acetate (Depo-Provera(R)), (3) a levonorgestrel intrauterine device (Mirena(R)), or (4) a copper intrauterine device (ParaGard(R)), plus 25 women using condoms alone. Cells from each participant will be collected from the cervix (using both cytobrush and biopsy), the endometrium, and peripheral blood at baseline (in the early follicular phase of their menstrual cycle) and after 3 and 6 months of contraceptive use. Cellular populations will be quantified using flow cytometry. Because genital tract microflora also impact mucosal immune cells within the genital tract, we will assess microflora of the lower and upper genital tract at each time point using culture-based and molecular methods. Characterizing changes in HIV target lymphocytes within the female genital tract associated with contraceptives could inform the design of future clinical trials assessing contraception and HIV risk as well as impact contraceptive recommendations for women at high risk of HIV exposure.